In so-called progressive die systems, workpieces formed from strip stock remain attached to webs that extend along lateral edges of the pieces to facilitate indexing of the workpieces through successive stages of the die assembly. Although such arrangements facilitate conveyance of workpieces through the die stations, they possess the disadvantage that the workpieces must be formed in a linear array at spaced locations along the strip stock, leading to substantial inefficiency and waste. Furthermore, the fact that all workpieces remain interconnected during at least a major portion of the die operation can lead to difficulty and inefficiency in performing operations on the workpieces at a given station. For these reasons and others, so-called die transfer systems have been developed in which the workpieces are pre-separated and fed to individual units of the die arrangement. A die transfer system of this character permits more efficient use of the strip stock material, and also permits greater flexibility in operations that can be performed at the individual die stations. However, the conveyor arrangement for indexing individual workpieces through a die transfer system is more complex than those in typical progressive die systems, usually involving release and re-engagement with the workpieces at each of the individual die stations.
U.S. Pat. No. 5,136,874, assigned to the assignee hereof, discloses a die transfer system that includes a lower die, an upper die carried for reciprocal vertical movement toward and away from the lower die to perform at least one operation on a workpiece positioned therebetween, and a conveyor arrangement for sequentially conveying workpieces between the dies. The conveyor arrangement has a pair of conveyors disposed on opposite lateral sides of the lower die. Each conveyor includes a plurality of hands for gripping workpieces, with the hands being spaced from each other lengthwise of the conveyor by distances corresponding to stations of the die. Each conveyor and its associated hands are indexed in a longitudinal direction through the die between stations in synchronism with motion of the upper die. The hands are moved simultaneously in at least one direction perpendicular to the longitudinal indexing direction by a camshaft that extends through the stations along an axis parallel to the indexing direction. A cam is mounted on each camshaft for rotation with the camshaft in synchronism with motion of the upper die. A follower arrangement couples each cam to the hands of the associated conveyor, so that reciprocal rotation of the camshaft about its axis results in reciprocal motion of the hands in one or more directions lateral to the longitudinal direction of conveyance of workpieces through the die stations. The conveyor camshafts are rotated by cam-and-follower arrangements coupled to the upper die, or by electric servo motors controlled by a master controller.
Although the die transfer system and indexing conveyor arrangement disclosed in the noted patent address and overcome problems and deficiencies theretofore extant in the art, further improvements remain desirable. For example, it is occasionally desirable to afford operator access to the workpiece hands of the conveyor and/or to the forming elements of the die either for purposes of maintenance, or for purposes of change-over to workpieces of different configuration. A general object of the present invention, therefore, is to provide a die transfer system of the character described above that features an improved conveyor arrangement with facility for providing operator access to the conveyor and/or lower die for maintenance, repair and/or change-over purposes and the like. Another and more specific object of the present invention is to provide a die transfer system of the described character that is economical in construction.